A coil spring can roughly be sorted, in accordance with kinds of loads applied thereon, into four kinds of springs of compression coil spring, tension coil spring, torsion coil spring and coil spring to which irregular load different from above three kinds of loads is applied respectively, having diversified shapes. Herein, however, accuracy of number of active coils is most important for any kind of coil spring because such active coils store strain energy in accordance with a load applied thereto. Accordingly, it is most important for manufacture of coil spring how to enhance accuracy of the active coils and how to improve the manufacturing speed.
A coil spring manufacturing apparatus can be classified into following two types of apparatus.
(1) A coil spring manufacturing apparatus of a core bar driving system wherein a wire material is wound closely or with a pitch around the circumference of the core bar while it is pulled in parallel with the process that said core bar providing a protrusion which is capable of holding the end of wire material used for forming a coil when it is inserted thereto is rotated and moved in the axial direction, and thereafter the total coils are formed by rewinding the wire material at the specified timing.
(2) A coil spring manufacturing apparatus of a pressurizingly operated co-roller driving type wherein the total coils are formed through solid winding or pitch winding of wire material by forming continuously in the specified radius of curvature while the wire material pressurizingly sent through rotation of more than one set of the pressurized feed co-rollers is pressed to a bending dies through a wire guide or by changing inter-relation of bending dies to the wire material by operating a pitch tool in accordance with necessity.
As described above, a coil spring manufacturing apparatus in any kind is composed of a driving mechanism which drives and rotates a core bar or a pressurized feed co-roller for supplying a wire material to a coil forming part in order to form the total coils of coil spring and a pitch changing means for moving the core bar in the axial direction or changing relative position of bending dies to the wire material in order to change the pitch of active coils of coil spring, a means for forming the end part of coil spring like the aforementioned pitch changing means in order to change the pitch of end turn of coil spring, a means for forming a hook of the end part of coil spring, a means for changing cross-sectional shape of the active coils which move position of dies in order to change cross-sectional shape of the active coils of coil spring in such a case where a coil spring having the cross-sectional shape like a barrel is to be formed, and a wire material cutting means (hereinafter these means are called forming means). The former driving mechanism and the latter driving mechanism of the forming means are sequentially operated through cams, rotating shafts, gears and link mechanisms.
However, in the conventional coil spring manufacturing apparatus, the driving mechanism for forming a total coils of coil spring employs, as the basic driving mechanism principle, a system where a pinion is caused to make a reciprocal rotation by giving a reciprocal movement to a sector gear or rack through the rotation of crank or cam which is capable of ensuring a comparatively large number of coils and expanded length within the limited period and also economical simple harmonic motion curve. In general, in the case of pressurized feed co-roller driving system, an intermittent rotation in one direction is transmitted to the clutch shaft through the main one-way clutch and one-way clutch for back stop fixed to the pinion which makes reciprocal rotation and moreover a wire material is fed with pressure by the pressurized feed co-roller through rotation of the pressurized feed co-roller shafts by means of plural sheets of conjugated acceleration gears, however, it is also possible to complementally feed a wire material with pressure for a short period by connecting, for the auxiliary feed, a cam and a link mechanism operated by said cam to the abovementioned one-way clutch for back stop. In the case of the core bar driving system, on the other hand, as is already disclosed in the Patent Applications Laid-Open Nos. 1354/1976 and 69562/1979, the prescribed object is attained by employing many gears and links and hydraulic apparatus, but these patent applications have following disadvantages. Namely,
(1) An over-running caused by a force of inertia of related link mechanism, gear and shaft makes difficult the accurate control and accurate control is difficult due to influence of backlash provided to gears. Therefore, accuracy of a number of coils and feed length of wire of coil spring manufactured is low.
(2) The stopper mechanism or brake mechanism and a mechanism for operating such mechanism in the specified timing are necessary in order to improve such low accuracy. Accordingly, a coil spring manufacturing apparatus is complicated and becomes expensive and moreover requires troublesome maintenance and control.
(3) Many mechanical parts such as related link mechanisms, gears and shafts are used and thereby it is difficult to quickly start high-speed driving and to enhance manufacturing capability of coil spring. When high speed driving is carried out, a force of inertia of mechanical parts becomes large, accuracy is deteriorated greatly and moreover a failure rate increases due to damage of mechanical parts.
(4) Since many mechanisms are combined, operating procedures are complicated and trial and error must be experienced by several reciprocal operations in order to change a number of coils and feed length of wire of coil spring.
(5) A driving time of driving mechanism for forming the total coils of coil spring during a turn of the principal driving shaft of machine is fixed, there are much restrictions on the diversified application field of coil spring manufacturing apparatus. Thereby, it is difficult to form a coil spring having a large number of coils and a long feed length of wire. Simultaneously, it is difficult to take a longer time for driving the forming means and to form a coil spring having complicated shape of end portion.
As described above, the conventional coil spring manufacturing apparatus has various disadvantages and these disadvantages have been attributed to a driving mechanism which supplies a wire material to a coil forming part in order to form the total coils of coil spring. Thus, in view of eliminating the aforementioned disadvantages, a numerically-controlled coil spring manufacturing apparatus has been developed. In such an apparatus, a driving mechanism which supplies a wire material to the coil forming part in order to form the total coils of coil spring is not driven by driving force of the main driving shaft of a machine through respective mechanisms but is driven by another driving mechanism independent of said main driving shaft in synchronization with the driving of forming means.
However, such a numerically-controlled coil spring manufacturing apparatus has following practical defects that it is difficult to easily, economically and accurately synchronize such driving mechanism and rotation of the principal shaft of a mechanism for driving the forming means even in case of changing the specification of coil spring to be manufactured, and productivity is rather deteriorated due to increase in cost and low driving speed in comparison with high speed operation, accuracy, cost reduction and versatility of the simplified forming means in the conventional coil spring manufacturing apparatus which is mainly driven by various operations of forming cams which are driven by a general purpose power motor which rotates continuously at a constant rate. Such a numerically-controlled coil spring manufacturing apparatus is not desirable for productivity in the following point that in case a DC servo motor is driven, when a command pulse train is input as shown in FIG. 1, pulses are counted and accumulated by a deviation counter of the positioning control circuit. It is then converted to DC analogue voltage by a digital-analogue converter and it becomes a speed command of servo pack owing to the control circuit. Thereby a DC servo motor is driven. In synchronization with such driving, an optical tachometer directly connected to the motor shaft generates pulses proportional to a rotating angle of the motor shaft and thereby the pulses in the deviation counter are subtracted. Thereby, if the constant command pulses are continuously input, a DC servo motor continues steady rotation, but a DC servo motor continues rotation until the pulses in the deviation counter becomes zero even when there is no input of command pulse as shown in FIG. 2. Accordingly, a large difference is generated between rotation of DC servo motor and command pulses.
Namely, a DC servo motor cannot rapidly reach the rotating speed which is proportional to a frequency of command pulse due to a force of inertia of the rotating part of servo motor and that of devices to be driven and is delayed as much as the content accumulated in the deviation counter. Such amount of content, namely delay of rotation, becomes large as the frequency of command pulse becomes high, in other words, the number of rotation of servo motor becomes high. As a result, it is impossible for the coil spring manufacturing apparatus to synchronize the driving mechanism which supplies a wire material to the coil forming part in order to form the total coils of coil spring and the driving mechanism of forming means. However, it may become possible to synchronize a DC servo motor for supplying a wire material to the coil forming part and the forming means by increasing or decreasing the frequency of command pulse train using a very high speed computer, but it is not desirable because employment of such high speed computer makes considerably expensive apparatus.
The inventor of the present invention does not intend to employ a numerical control which results in increase of cost and low operation speed but have perceived that improvement is required for the driving mechanism which supplies a wire material to the coil forming part in order to form the total coils of coil spring. Accordingly, the inventor does not employ a complicated NC system isolated from the coil spring manufacturing apparatus and have succeeded in development of an economical numerically-controlled coil spring manufacturing apparatus which directly utilizes characteristics such as high speed operation, high accuracy, cost reduction and versatility of the simplified forming means in the widely used conventional coil spring manufacturing apparatus which is mainly driven by operations of various forming cams which are driven by a general purpose power motor which rotates continuously at the constant rate and a simplified mechanism which always can synchronize with a wide range of rotation from very low irregular speed rotation by manual driving required for changing the number of coils or feed length of wire of coil spring to a speed rotation as high as about 350 rpm, for example.